1. Field of the Invention
Embodiments of the present invention relate, in general, to power grids and more particularly to systems and methods for controlling allocation, production, and consumption of power in an electric power grid.
2. Relevant Background
An electrical grid is not a single entity but an aggregate of multiple networks and multiple power generation companies with multiple operators employing varying levels of communication and coordination, most of which are manually controlled. A smart grid increases connectivity, automation and coordination among power suppliers and power consumers and the networks that carry that power for performing either long-distance transmissions or local distribution.
Today's alternating current power grid was designed in the latter part of the 19th century. Many of the implementation decisions and assumptions that were made then are still in use today. For example, the current power grid includes a centralized unidirectional electric power transmission system that is demand driven. Over the past 50 years the electrical grid has not kept pace with modern challenges. Challenges such as security threats, national goals to employ alternative energy power generation, conservation goals, a need to control peak demand surges, uninterruptible demand of power, and new digital control devices put in question the ability of today's electrical distribution grid. To better understand the nature of these challenges, a firm grasp of current power generation and distribution is necessary.
The existing power grid starts at a power generation plant and thereafter distributes electricity through a variety of power transmission lines to the power consumer. The power producer or supplier in almost all cases consists of a spinning electrical generator. Sometimes the spinning generators are driven by a hydroelectric dam, large diesel engines or gas turbines, but in most cases the generator is powered by steam. The steam may be created by burning coal, oil, natural gas or in some cases a nuclear reactor. Electric power can also be produced by chemical reactions, direct conversion from sunlight and many other means.
The power produced by these generators is alternating current. Unlike direct current, alternating current oscillates much like a sine wave over a period of time. Alternating current (AC) operating as a single sine wave is called single phase power. Existing power plants and transmission lines carry three different phases of AC power simultaneously. Each of these phases is offset 120° from each other and each phase is distributed separately. As power is added to the grid, it must be synchronized with the existing phase of the particular transmission line it is utilizing.
As this three-phase power leaves the generator from a power station, it enters a transmission substation where the generated voltage is up-converted to an extremely high number for long-distance transmission. Then, upon reaching a regional distribution area, the high transmission voltage is stepped down to accommodate a local or regional distribution grid. This step down process may happen in several phases and usually occurs at a power substation.
FIG. 1 shows a typical power distribution grid as is known to one skilled in the art. As shown, three power generation plants 110 service three distinct and separate regions of power consumers 150. Each power plant 110 is coupled to its power consumer 150 via distribution lines 140. Interposed between the power producer 110 and the power consumer 150 are one or more transmission substations 125 and power sub-stations 130. FIG. 1 also shows that the power production plants are linked via high-voltage transmission lines 120.
From each power production plant 110, power is distributed to the transmission substation 125 and thereafter, stepped down to the power substations 130 which interface with a distribution bus, placing electricity on a standard line voltage of approximately 7200 volts. These power lines are commonly seen throughout neighborhoods across the world, and carry power to the end-user 150. Households and most businesses require only one of the three phases of power that are typically carried by the power lines. Before reaching each house, a distribution transformer reduces the 7200 volts down to approximately 240 volts and converts it to normal household electrical service.
The current power distribution system involves multiple entities. For example, production of power may represent one entity; while the long distance transmission of power another. Each of these companies interacts with one or more distribution networks that ultimately deliver power to the power consumer. While the divisions of control described herein are not absolute, they nonetheless represent a hurdle for dynamic control of power over a distributed power grid.
Under the current power distribution grid, should the demand for power by a group of power consumers exceed the production capability of their associated power production facility, that facility can purchase excess power from other producers of networked power. There is a limit to the distance power can be reliably and efficiently transported, thus as consumer demand increases, more regional power producers are required. The consumer has little control over who produces the power it consumes.
Electrical distribution grids of this type have been in existence and use for over 100 years. And while the overall concept has not significantly changed, it has become extremely pervasive and has been reasonably reliable. However, it is becoming increasingly clear that the existing power grid is antiquated, and that new and innovative control systems are necessary to modify the means by which power is efficiently distributed from the producer to the consumer. For example, when consumer demand for power routinely exceeds the production capability of a local power production facility, the owner and operator of the local power network considers adding additional power production capability, or alternatively, a portion of the consumers are denied service, i.e. brown-outs. To add additional power to the grid, a complicated and slow process is undertaken to understand and control new electrical power distribution options. The capability of the grid to handle the peak demands must be known and monitored to ensure safe operation of the grid, and, if necessary, additional infrastructure must be put in place. This process can take years and fails to consider the dynamic nature of electrical production and demand.
One aspect highlighting the need to modify existing power distribution control systems is the emergence of alternative and renewable power production sources, distributed storage systems, demand management systems, smart appliances, and intelligent devices for network management. These options each require active power management of the distribution network, substantially augmenting the control strategies that are currently utilized for distribution power network management.
Existing network management solutions lack the distributed intelligence to manage power flow across the network on a multitude of timescales. This void is especially evident, since new power generation assets being connected to the grid are typically owned by different organizations and can be used for delivering different benefits to different parties at different times. Conventional electric power system management tools are designed to operate network equipment and systems owned by the network operators themselves. They are not designed to enable dynamic transactions between end-users (power consumers), service providers, network operators, power producers, and other market participants.
Existing power grids were designed for one-way flow of electricity and if a local sub-network or region generates more power than it is consuming, the reverse flow of electricity can raise safety and reliability issues. A challenge, therefore, exists to dynamically manage power production and network assets in real time, and to enable dynamic transactions between various energy consumers, asset owners, service providers, market participants, and network operators. Since changes have to be made to the existing electric power system to add dynamic power management capabilities using different resources and under various conditions, an additional challenge exists to model and simulate the behavior of the power system using different power management strategies. These and other challenges present in the current power distribution grid are addressed by one or more embodiments of the present invention.